70 ROOT-KNOT AND ITS CONTROL. 



variety being usually sufficiently resistant to the root-knot to permit 

 its use for this purpose. In the fall this can be cut for seed or hay. 

 The ground should then be plowed up and the process repeated the 

 next season. Except in exceedingly bad infestations, two seasons 

 devoted to Iron cowpeas should be sufficient to free the land from the 

 pest. If desired, some winter grain, preferably rye or perhaps wheat, 

 may be sown in the fall, the cowpeas not being planted until the crop 

 is harvested early the next summer, following them by grain again. 

 Where the weather remains warm rather late in the fall it would be 

 desirable always to do this and so prevent the growth of weeds 

 which might harbor the nematode in the fall and winter. Where 

 the summer is long enough, velvet beans or Florida beggarweed are 

 perhaps preferable to cowpeas, as they give a denser growth that more 

 completely smothers out all weeds. Special care must be taken that 

 in the summer time no weeds are allowed to grow in the field, as it 

 will be seen by reference to the list of susceptible plants that many 

 of the common weeds harbor the nematode. Their presence in the 

 field, therefore, would serve to perpetuate rather than kill the 

 nematode. 



Where practicable, the surest results can be attained by keeping 

 the ground absolutely bare of all vegetation for two years. This can 

 not be done on some soils, owing to the danger of the destruction of 

 humus by the hot sun or of washing by heavy rain. 



Wliere the field is free from roots of perennial plants which might 

 shelter the pest and is so situated that it can be submerged easily 

 for long periods, it may pay to flood the land for three or four weeks, or 

 perhaps during the winter. This would be impracticable except in a 

 few locations. Furthermore, in many soils it would leach out all the 

 plant food and make the soil poor, but where an impermeable layer 

 will hold the water and keep it from leaching out it is conceivable 

 that this method might be found very satisfactory. A short period 

 of floodmg or attemptmg to do this while the soil contains perennial 

 roots contauiing the nematode will hardly prove successful. 



In the irrigated districts of the West, special care should be taken 

 to avoid the introduction of this nematode into lands devoted to 

 potato raising. To tliis end only perfectly sound, clean potatoes 

 should be used; no potatoes from suspected regions should be planted, 

 even should the individual potatoes appear perfectly healthy, with- 

 out a preluninary sterilization with formaldehyde solution to destroy 

 any nematodes present in the adhering soil. 



Should none of the foregoing methods be feasible, high fertiliza- 

 tion, especially with that element (potassium calcium or phos- 

 phorus) which is most nearly deficient in the soil, will prove helpful, 

 although it will not kill the nematodes. When, as is often the case in 



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